Ricco et al. (Hum. Genet. 32, 305, 1976) have reported the presence of threonine instead of isoleucine at position 75 in part of the gamma chains in some samples of human hemoglobin F. Their work has been substantiated and extended during the past year. Because of the availability of hundreds of samples from prior studies of Hb-F in normal and abnormal hematological conditions, major effort during the next year will be the study of this new aspect of Hb-F in an effort to determine its relationship in the genetics and control of the linked beta, gamma and delta genes. These studies will be made in collaboration with Prof. T. H. J. Huisman of the Medical College of Georgia.